The present invention relates to crane mechanisms, and more particularly, to crane mechanisms adapted for use on tow trucks and other similar vehicles.
In the prior art, the mobile cranes associated with wrecker trucks for towing other vehicles, or which are utilized for lifting heavy loads from inaccessible places and transporting the same to more appropriate positions for further handling, have employed mechanical winches for lifting the load and other mechanical winches in conjunction with a boom for further positioning of a load. The maximum safe load limit for these mechanical arrangements is generally determined by the mass of the material used in the mechanical devices such as cable diameters, thicknesses of structural steel for the boom and supports therefor, sizes of bolts and pivots, etc.
In these crane designs of the prior art, very little consideration is given to the employment of mechanical advantages to structural parts which would increase the load limits while still staying within all of the safety factors required for wrecker or tow vehicles. For example, the most common wrecker truck, the Holmes 600, has a rather limited maximum load specification for the structure and equipment employed. This particular wrecker truck utilizes hand crank winches to extend and retract a boom and also to adjust its angular orientation during hoisting operations. The boom is anchored for pivotal movement and supported by various bracing members in an arrangement which is not efficient in terms of load capacity and cost for the load to which the arrangement is capable of handling.
The present invention has been devised to overcome the disadvantages pointed out above by (1) utilizing hydraulic rams as the power driven mechanisms for boom manipulation and extension and (2) to arrange the rams, the boom and supporting structure therefor to be more efficient in terms of maximum loads, the capacity for which the invention is capable and involving lower cost for this increased efficiency and load capacity. For example, the mobile crane devised in accordance with the present invention can be considered as a direct replacement for the conventional Holmes 600 wrecker crane, and while this crane has a rated maximum capacity of 16 tons, the present invention associated with the same host vehicle has a rated capacity of 25 tons.
In order to accomplish this efficiency and increase the maximum capacity, the present invention utilizes a hoisting boom having an inner square tube member telescoping within an outer square tube member and a hydraulic ram arranged within the boom members for extending and retracting the inner member.
The boom is pivoted at one end on the flat bed of a host truck utilizing a novel pivoting device for distributing the great forces experienced by the boom along its longitudinal axis more evenly along the truck bed. A pair of hydraulic rams are supported on the flat bed for driving and controlling the angular movements of the boom during hoisting operations, the same being oriented to provide maximum mechanical advantage for these operations thereby effecting maximum efficiency out of these devices for the purposes intended. Each of the rams are served by a hydraulic circuitry which will insure safety with no disturbance to the boom and therefore the load being manipulated in the event of hydraulic failure.
It is the principle object of the present invention to employ hydraulic rams as the power drive mechanism for a mobile wrecker or tow vehicle and thereby increase the maximum load capacity therefor.
Another object of the invention is to increase the efficiency of a mobile crane by arranging the hoisting and moving devices associated with the crane in a manner wherein maximum mechanical advantages may be employed.
These and other objects of the invention will become apparent after reading the following description taken in conjunction with the accompanying drawings.